The present invention relates to a semiconductor device in which a stack of semiconductor chips is mounted on a wiring board.
Recently, to downsize electronic units and improve the reliability thereof, a semiconductor device in which multiple semiconductor chips are included in one package has been in high demand. In view of this, to realize high performance and high packaging density, a semiconductor device (an LSI package) made by stacking a plurality of semiconductor chips on a wiring board has attracted more and more attention.
Hereinafter, a known semiconductor device will be described with reference to the drawing.
FIG. 6 shows a cross-sectional structure for a known semiconductor device with a stack of LSI chips. As shown in FIG. 6, first and second LSI chips 102 and 103 are secured to each other on a wiring board 101 so that the non-circuitry sides of these chips 102 and 103 face each other, i.e., so that the top of the chip 102 faces the bottom of the chip 103.
The circuitry side of the first LSI chip 102 faces the principal surface of the wiring board 101 and is electrically (connected to the wiring board 101 via raised electrodes 104. In other words, the first LSI chip 102 is flip-chip bonded to the wiring board 101. External electrodes 105 on the circuitry side of the second LSI chip 103 are electrically connected to the wiring board 102 via metal fine wires 106.
However, in the known semiconductor device, because of recent remarkable increase in number of pins in an LSI chip, the external electrodes 105 on the second LSI chip 103 are often located almost right over the raised electrodes 104 on the first LSI chip 102 as viewed vertically downward from over the principal surface of the wiring board 101. Thus, during a wire bonding process in which the external electrodes on the second LSI chip 103 are bonded to the wiring board 101, if a load is applied downward vertically to the principal surface of the wiring board 101 with a bonding jig, the raised electrodes 104 and surrounding portions thereof (which will be herein referred to as xe2x80x9cflip-chip bonding terminalsxe2x80x9d) are mechanically damaged. As a result, the electrical connection between the first LSI chip 102 and wiring board 101 via the raised electrodes 104 deteriorates due to the mechanical damage or the bonding terminals might be crushed. That is to say, if the thicknesses of the LSI chips 102 and 103 are reduced to 300 xcexcm or less to meet the demand of thinning a semiconductor device, it should be difficult for the thinner LSI chips 102 and 103 to internally attenuate the load applied thereto by the bonding jig.
In addition, even if a low-melting metal with a mechanical strength greater than that of a conductive adhesive or resin is used for the raised electrodes 104, the mechanical strength of the bonding terminals will not increase so much as compared to the bonding terminals made of the conductive adhesive or resin. This is because the size of the raised electrodes 104 is several tens xcexcm at the most.
Further, the first and second LSI chips 102 and 103 are secured together so that their non-circuitry sides face each other. Thus, it is difficult to mount a stack of three or more LSI chips on one wiring board 101. Accordingly, it is not so easy for the know techniques to further improve the performance and further increase packaging density.
It is therefore an object of the present invention to solve these problems of a semiconductor device with a stack of multiple semiconductor chips. Specifically, a first object of the present invention is to establish more reliable electrical connection by suppressing the deterioration of the flip-chip bonding terminals during a wire bonding process. A second object of the present invention is to get three or more semiconductor chips mounted on a wiring board.
To achieve the first object, a first inventive semiconductor device includes: a wiring board; a first semiconductor chip, which has a circuitry side and a non-circuitry side that face each other vertically and which is electrically connected to the wiring board via a raised electrode, the circuitry side of the first chip facing the principal surface of the wiring board; and a second semiconductor chip, which has a circuitry side and a non-circuitry side that face each other vertically and which includes an external electrode on the circuitry side thereof. The non-circuitry sides of the first and second semiconductor chips are secured to each other. The external electrode of the second semiconductor chip is connected to the wiring board via a metal fine wire. The external and raised electrodes are so disposed as not to overlap each other as viewed vertically downward from over the principal surface of the wiring board.
In the first inventive semiconductor device, the external and raised electrodes are so disposed as not to overlap each other as viewed vertically downward from over the principal surface of the wiring board. Thus, the load applied to the external electrode during a wire bonding process does not propagate to a flip-chip bonding terminal on the first semi-conductor chip so easily. As a result, electrical connection does not deteriorate at the flip-chip bonding terminal.
To achieve the second object, a second inventive semi-conductor device includes: a wiring board; a first semi-conductor chip, which has a circuitry side and a non-circuitry side that face each other vertically and which is electrically connected to the wiring board via a raised electrode, the circuitry side of the first chip facing the principal surface of the wiring board; and at least second and third semiconductor chips, each of which has a circuitry side and a non-circuitry side that face each other vertically and each of which includes an external electrode on the circuitry side thereof. The non-circuitry sides of the second and third semiconductor chips are secured to the non-circuitry side of the first semiconductor chip. The external electrodes of the second and third semiconductor chips are connected to the wiring board via metal fine wires.
In the second inventive semiconductor device, the non-circuitry sides of the second and third semiconductor chips are secured to the non-circuitry side of the first semiconductor chip. Thus, a stack of three or more semiconductor chips can be mounted on the wiring board. As a result, high performance and high packaging density are realized.
To obtain the second object, a third inventive semiconductor device includes: a wiring board; at least first and second semiconductor chips, each of which has a circuitry side and a non-circuitry side that face each other vertically and each of which is electrically connected to the wiring board via a raised electrode, the circuitry sides of the first and second chips facing the principal surface of the wiring board; and a third semiconductor chip, which has a circuitry side and a non-circuitry side that face each other vertically and which includes an external electrode on the circuitry side thereof. The non-circuitry side of the third semiconductor chip is secured to the non-circuitry side of the first semiconductor chip and/or the non-circuitry side of the second semiconductor chip. The external electrode of the third semiconductor chip is connected to the wiring board via a metal fine wire.
The third inventive semiconductor device includes at least the first and second semiconductor chips which are electrically connected to the wiring board via raised electrodes. In this device, the non-circuitry side of the third semiconductor chip is secured to the non-circuitry side of the first semiconductor chip and/or the non-circuitry side of the second semiconductor chip. Thus, a stack of three or more semiconductor chips can be mounted on the wiring board. As a result, high performance and high packaging density are realized.
In the second or third semiconductor device, the external and raised electrodes are preferably so disposed as not to overlap each other as viewed vertically downward from over the principal surface of the wiring board. Then, the load applied to the external electrode during a wire bonding process does not propagate to a flip-chip bonding terminal on the first semiconductor chip so easily. As a result, electrical connection does not deteriorate at the flip-chip bonding terminal. Thus, the first object is also accomplished.
In one embodiment of the present invention, the raised electrode(s) and the wiring board may be secured to each other with a conductive adhesive. Then, the raised electrode(s) and the wiring board can be bonded together with the conductive adhesive at a relatively low temperature of about 100xc2x0 C. Thus, no thermal stress is created in the first (or second) semiconductor chip or the wiring board. As a result, no mechanical damage is caused due to bending of the chip or the board.
Alternatively, the raised electrode(s) and the wiring board may be secured to each other with a low-melting metal. Then, bonding strength increases between the wiring board and the first (and second) semiconductor chip(s).
As another alternative, the raised electrode(s) may be in direct contact with (an) interconnector electrode(s) formed on the wiring board. Then, even if the raised electrodes are arranged at a narrow pitch on the first (and second) semiconductor chip(s), no electrical short circuit will be caused by any adhesive. As used herein, the interconnector electrodes are parts of the wiring on the wiring board and are bonded to the raised electrodes.